Default Namespaces : Namespace « Namespace « XML Tutorial

A default namespace is like a regular namespace.
You don't have to specify a prefix for all of the elements that use it.
<person xmlns="http://www.java2s.com">
<name>
<title>Sir</title>
</name>
</person>
You can declare more than one namespace for an element, but only one can be the default.
<person xmlns="http://www.java2s.com"
xmlns:xhtml="http://www.w3.org/1999/xhtml">
<name/>
<xhtml:p>This is XHTML</xhtml:p>
</person>